Generally, a plasma display panel (referred to hereinafter simply as a “PDP”) is a display device which displays images with phosphors excited by the plasma discharge. When voltages are applied to the electrodes arranged within the discharge space of the PDP, a plasma discharge is generated between the electrodes and generates ultraviolet rays. The ultraviolet rays excite the phosphors with a predetermined pattern, thereby displaying the desired images.
A PDP is generally classified as an AC-type, a DC-type or a hybrid-type. FIG. 4 is an exploded perspective view of a discharge cell for a common AC-type PDP. As shown in FIG. 4, the PDP 100 includes a bottom substrate 111, a plurality of address electrodes 115 formed on the bottom substrate 111, a dielectric layer 119 formed on the bottom substrate 111 over the address electrodes 115, a plurality of barrier ribs 123 formed on the dielectric layer 119 and phosphor layers 125 formed between the barrier ribs 123. The barrier ribs maintain the discharge distance and prevent cross talk between the cells.
A plurality of discharge sustain electrodes 117 are formed on the lower surface of a top substrate 113 facing the bottom substrate 111 and spaced apart from the address electrodes 115 formed on the bottom substrate 111. The address electrodes are oriented perpendicular to the sustain electrodes. A dielectric layer 121 and a protective layer 127 sequentially cover the discharge sustain electrodes 117 on the side opposite the top substrate. While other materials may be used, the protective layer 127 is often formed of MgO.
The MgO protective layer is a transparent thin film, which reduces the effect of the ion collision caused by the discharge gas during operation, thereby protecting the dielectric layer. The MgO layer also emits secondary electrons so that the discharge voltage is lowered. The MgO protective layer is generally formed on the dielectric layer to a thickness of 3000-7000 Å. The MgO protective layer is generally formed using a sputtering method, electron beam deposition, ion beam assisted deposition (IBAD), chemical vapor deposition (CVD), or a sol-gel method. Recently, an ion plating method has been developed and has been used to form a MgO protective layer.
With regard to the electron beam deposition method, electron beams accelerated by electromagnetic fields collide against the MgO deposition material in order to heat and vaporize it, thereby forming a MgO protective layer. Although the sputtering method is preferred over the electron beam deposition method because the resulting protective layer is more densely formed with favorable crystalline alignment, the production costs are unfavorably high For the sol-gel method, the MgO protective layer is formed from a liquid phase.
As an alternative to these various methods for forming a MgO protective layer, an ion plating method has been recently developed. In the ion plating method, vaporized particles are ionized and form a target layer. Although the ion plating method is similar to the sputtering method with respect to the adhesion and crystallinity of the MgO protective layer, there is an advantage in that it is capable of rather high speed deposition at 8 nm/s.
According to such a processes, single crystal of MgO or sintered MgO is used. However, it is difficult to control the suitable amount of a specific dopant due to the difference of the solid solution limit in cooling process to manufacture a single crystal of MgO. Namely, a specific dopant for controlling the quality of MgO layer is precipitated without being solved in a single crystal of MgO during cooling process. For this reason, the MgO protective layer is generally formed by the ion plating method using a sintered MgO combined with a suitable amount of an appropriate dopant. Pellet-shaped materials may be used to deposit the MgO protective layer. The dissolution speed of the MgO generally depends upon the size and the shape of the pellets. Therefore, various attempts have been made to optimize the size and the shape of the MgO pellets.